Hydrogenated block copolymers of butadiene and isoprene

Abstract

The products disclosed herein involve hydrogenated butadiene-isoprene block copolymers having at least five alternating blocks of the two respective monomers. Such hydrogenated block copolymers have an improved permanent set or lower residual strain as compared to similar hydrogenated block copolymers having only three such alternating blocks. Moreover, a milled product made from such material has a much improved smoothness of surface. These new products are particularly useful in making rubber hose, shoe soles, etc. and are also useful for blending with polyolefins, such as polyethylene, to improve the impact resistance of polyolefin resins without sacrifice of rigidity.

The invention claimed is: 
     
       1. A hydrogenated block copolymer of improved permanent set and related properties comprising essentially at least 5-15 alternating blocks of hydrogenated butadiene and hydrogenated isoprene, which hydrogenated isoprene block may contain up to 50 percent by weight of hydrogenated butadiene, the hydrogenated butadiene portions representing 5-70 percent by weight and the hydrogenated isoprene portions representing 30-95 percent by weight, based on the total copolymer weight, each block of said copolymer being equivalent to a molecular weight of 1,000-100,000. 
     
     
       2. The copolymer of claim 1 in which there are at least seven said blocks. 
     
     
       3. The copolymer of claim 1 in which there are 5-11 of said alternating blocks. 
     
     
       4. The copolymer of claim 1 in which each block is equivalent to a molecular weight of 2,000-50,000. 
     
     
       5. The copolymer of claim 1 in which there is 20-80 percent by weight of hydrogenated isoprene. 
     
     
       6. A polyolefin composition of improved impact strength comprising 10-95 percent by weight of a polymer of an alpha-olefin having 2-4 carbon atoms and 5-90 percent by weight of the hydrogenated block copolymer of claim 1. 
     
     
       7. The composition of claim 6 in which said polyolefin is polyethylene. 
     
     
       8. The composition of claim 6 in which said polyolefin is polypropylene. 
     
     
       9. The composition of claim 6 which contains 15-60 percent by weight of said hydrogenated block copolymer. 
     
     
       10. The copolymer of claim 1 in which said hydrogenated isoprene blocks consist of hydrogenated isoprene homopolymer blocks. 
     
     
       11. The copolymer of claim 1 in which said hydrogenated isoprene blocks also contain hydrogenated butadiene up to 50 percent by weight of each said block.